The confronting cisternae in neurons in the substantia gelatinosa of the spinal cord of rats and Japanese monkeys.

The neurons in the substantia gelatinosa of the spinal cord of the rat and Japanese monkey were investigated electron microscopically and ultracytochemically. The confronting cisternae observed in the cytoplasm of the majority of gelatinosal neurons in both species were composed of closely apposed parallel cisternae with electron-dense flocculent material, and a continuity with the cisternae of the rough endoplasmic reticulum was often observed. Ultracytochemically, the p-nitrophenylphosphatase (p-NPPase) activity was present in the confronting cisternae, but thiamine monophosphatase (TMPase) and thiamine pyrophosphatase (TPPase) activities were absent. These results indicate that the confronting cisternae are a variant of the rough endoplasmic reticulum.